Barbiturates and benzodiazepines produce their effects by exciting the activity of gamma-aminobutyric acid (GABA). GABA is the major inhibitory neurotransmitter (messenger chemical) in the central nervous system (CNS.) When its effects are "excited" it means that more inhibition occurs; in other words, more slowing of the CNS’ actions occurs. The patient experiences sedation, muscle relaxation, relief from anxiety, anticonvulsant effects, decreased contractability of the heart, and dilated blood vessels.
Both barbiturates and benzodiazepines are separated into long-acting and short-acting groups. Short-acting means that the drug produces effects sooner and that the effects wear off sooner. The short-acting drugs are generally more quickly addictive than the longer-acting drugs. In addition, withdrawal from short-acting tranquilizers can be more severe than from long-acting ones.